Cautious changes in Saudi Arabia over the last five years need to be followed by permanent institutional reforms or risk being eroded in future, Human Rights Watch (HRW) has warned in a report.

King Abdullah has "loosened the reins" that stifle Saudi society but has brought in few lasting improvements for women or in freedom of expression, judicial fairness or religious tolerance, argues the New York-based organisation.

On the positive side, the 85-year-old king, a close ally of the US, has promoted the modernisation of the state, encouraged a re-evaluation of the subservient status of women and religious minorities, and allowed greater debate in the media and promoted judicial fairness. But while the attitude toward change is now more "welcoming", this has not brought legislation, codification, enforcement or accountability.

Advances include allowing women to stay in hotels without male guardians, and to work in all fields "suitable to their nature". Women can also study law at university but cannot practise as lawyers in courts. Sex segregation is now less strict in public spaces such as restaurants and shopping malls, but Saudi women are not allowed to drive.

Under the guardianship system, women are legally minors and are unable to make basic decisions without a male guardian's consent, including decisions about marriage, education, employment, certain types of healthcare, or travel.

"Should [Abdullah's] enthusiasm for reform wane, or his successors tread more conservative paths, his legacy would be one of a brief respite of fresh air, but not one of institutional reform," said HRW.

Saudi reformers are opposed by conservatives, usually clerics, who defend the status quo to maintain their influence on the judiciary, education, Islamic affairs and public morality. Opposition also comes from the security establishment, which enforces bans on political parties, public rallies and organised strikes.

Judicial reforms have been implemented, but the 2009 trials of 331 terrorism suspects - an important test for due process - failed to meet basic standards of fairness since they were conducted summarily and in secret. Saudi Arabia still lacks a penal code, allowing judges "near-total" discretion to decide what behaviour constitutes a criminal offence. For example, judges have continued to jail and sentence people for witchcraft.

HRW found greater tolerance of criticism of the government. The Saudi press has also exposed abusive behaviour by the religious police, in one case expressing outrage at the arrest of a businesswoman who had gone to a Starbucks cafe to meet a male business partner. Still, the report says, there are clear limits to criticising an institution that is "intrinsically tied to the history and Islamic identity of Saudi Arabia".

The government also continues to control the appointment of editors and to punish those who criticise royals, government policies or senior clerics. "Any gains in free speech are subject to government whim," the report says. "King Abdullah's loosening of the restrictions on women and critical expression at times seem like tentative test flights by an elite as yet undecided about the type of government and society they want to steer toward."

Little tangible progress has been made towards greater religious tolerance, especially towards the kingdom's Shia Muslim minority. The same is true of the status and conditions of Saudi Arabia's 8 million migrant workers, who still require sponsorship and their employer's consent to change jobs or leave the country.

Informed views from other countries could help promote change, said HRW, but western media coverage is rarely helpful. "To be sure, scandals of eight-year-old brides and death sentences imposed on television fortune tellers for 'sorcery' reflect glaring Saudi failures to uphold and protect human rights," the report says. "But covering them alone fails to give a sense of what reforms are being debated, and indeed are possible, provided there is political will to do so."